BENDIX TCH-008-041 User Manual

Technical Bulletin

Bulletin No: Effective Date: Cancels: Page: 1 of
Subject:

The Bendix® AD-9™ air dryers are available with various purge valve confi gurations; hard seat, soft seat
and DLU discharge line unloader types. The difference between these types relates to the type of sealing
surface for the turbo cut-off valve. All AD-9™ air dryers contain two valve sections and have a rubber (soft)
seat for the actual purge valve, but the turbo cut-off valve section can be one of three types:

TCH-008-041

6-20-2006

Bendix® AD-9™ Air Dryer Purge Valve Identifi cation & Kits

N/A

3

Metal

Black

Hard Seat

Figure 1 - Identifi cation of Hard and Soft Seat Purge Valves

1. Hard seat purge valve has a metal to metal turbo cut-off valve sealing surface. Most AD-9
come standard with the hard seat purge valve.

2. Soft seat purge valve has a bonded rubber ring on the piston that contacts a metal seat on the housing
to make the turbo cut-off valve seal. This seal is extremely air tight for applications that require zero
leakage, such as the Bendix® EverFlow™ system and drop-in style air dryers which use older Holset
type E compressors.

3. Discharge line unloading (DLU) purge valve has the turbo cut-off valve bypassed by removing the
middle o-ring sealing surface from the body. This valve is used to positively vent the compressor
discharge line, such as when the vehicle has a non-unloading compressor.

NOTE: Although a soft seat purge valve can be substituted for a hard seat purge valve, a hard seat purge
valve should not be substituted for a soft seat purge valve. DLU purge valves cannot be substituted for any
other type.

© 2006 Bendix Commercial Vehicle Systems LLC All rights reserved. 6/2006 Printed in U.S.A.

Rubber

Soft Seat

™

air dryers

Bulletin No: Page: 2 of

TCH-008-041

3

3 o-rings

2 o-rings

Letter “U” stamped into

the body

Standard Style Purge

Valve

Figure 2 - Standard and DLU Purge Valves

DLU Style Purge Valve

Selecting the Purge Valve Replacement Kit for a Bendix® AD-9™ Air Dryer

When servicing your AD-9™ dryer with a purge valve replacement kit, you will need to identify the type of
purge valve being replaced. Removal of the purge valve from the dryer body is necessary to identify the
correct maintenance kit.

First, identify whether the purge valve is a DLU style. The DLU type can easily be distinguished from the
others, because the DLU type have only two o-rings on the outside of the purge valve body, rather than
the standard three o-rings. For DLU purge valves, the middle o-ring seat has been removed. Additionally,
AD-9™ air dryers with a DLU purge valve have the letter “U” stamped on the side of the purge valve housing.
Because the letter “U” is not always visible, it is best to use the number of o-ring grooves for identifi cation.
See fi gure 2.

If the purge valve is a standard style (not a DLU), look through the upper oval hole in the purge valve
housing to view the piston. If a black band encircling the piston is visible, then the purge valve is a soft
seat type. If the piston is all metal, then the purge valve is a hard seat. See fi gure 1 for hard and soft seat
purge valves.

After the purge valve type has been identifi ed, the next step is to identify the heater size; voltage and wattage.
The electrical connector on the purge valve is color coded as shown in the Purge Valve Replacement Kits
table on the following page.

Once the correct maintenance kit is identifi ed, service the purge valve following the instructions provided in
the kit for proper replacement.

Electrical Connector

Figure 3 - Voltage and Wattage

© 2006 Bendix Commercial Vehicle Systems LLC All rights reserved. 6/2006 Printed in U.S.A.